1. Field
This disclosure relates to an embedded visual inspection device and method to assess the extent of damage to a composite pressurized gas tank.
2. General Background
Motor vehicles may be fueled by gaseous fuels. Gaseous fuels are traditionally stored bound too chemical hydrides under low pressure or under higher pressure in tank structures. In transportation the weight of a vehicle, including fuel transporting vessels or tanks contributes to the Gross Vehicle Weight (GVW).
The heavier a vehicle the more force that is needed to propel it, to stop it and the less weight it can carry.
Storage of gaseous fuel cylinders/tanks in a tractor or trailer must meet crash safety requirements. Tank cylinders are measured in terms of burst pressure. If a cylinder has a 3000 psi rating it will have a burst strength (or failure rating) of 2-3 times that normal 3000 psi rating.
Gross Vehicle Weight Rating (GVWR). This is the rating that is calculated by the manufacturer as the amount of weight that the vehicle will be when the vehicle itself is weighed filled with fuel and loaded according to the manufacturer's specification.
Highway Weight. This is the legal weight related to highway size and weight limits. When operating on the interstate system, the maximum permissible weight is 20,000 lbs. on a single axle, 34,000 lbs. on a tandem axle, and 80,000 lbs. max gross weight. The “Bridge Formula” allows motor vehicles to be loaded to the maximum weight only if each group of axles on the vehicle and their spacing also satisfy the requirements of the formula. States must use these limits for their designated or national network highways. While the majority of the states use the federal bridge formula for all roads in their state, some do have a separate state formula for other state or county roads.
There is an ongoing balance between safety and weight with respect to pressurized fuel in motor vehicles Traditional methods of reducing tank weight have included using plastic lined tanks wrapped in fibers. These composite tanks weigh less than metal tanks but are more susceptible to damage from cuts, gashes and the like. Inspections of composite tanks for signs of damage are necessary but can be costly and time consuming. Determining whether damage to a tank is minor or major is a difficult task traditionally accomplished by taking the tank out of service and inspecting and measuring the damage. The first decision is made by the customer who may not be experienced enough to judge if anything is wrong. This lack of experience may result in hazardous situations.
Additionally, if a tank is to be used on a motor vehicle it must meet additional certifications such as NGV-2 certification. One requirement is that a tank is required to pass flaw test. The flaw test consists of a 1 inch long and minimum 0.05 inch deep cut in the tank and another one 8 inch long and minimum 0.03 inch deep.